Experimental study on hybrid concrete-filled fiber reinforced polymer tube (HCFFTs) columns under simulated seismic loading

Abstract

The concrete-filled fiber-reinforced polymer (FRP) tube (CFFT) system has been widely studied as a promising alternative to conventional reinforced concrete (RC) for the construction of bridge columns. While unreinforced CFFT columns are attractive for their ease of construction, their limited energy dissipation capabilities have restricted their application to seismic regions. The hybrid CFFT (HCFFT) system was introduced to address this shortcoming by incorporating steel reinforcement into the FRP shell in the form of 30-μm fibers. This system combines the ease of construction of conventional unreinforced CFFTs with the energy dissipation characteristics of lightly reinforced CFFT columns. This study reports the first experimental investigation on the seismic performance of HCFFT columns through large-scale testing of two columns under combined axial compression and cyclic lateral loading. Two shear loading conditions were studied. The flexural capacity, mode of failure, residual deformation, and energy dissipation capacity were evaluated. The low-shear specimen reached a drift ratio of 10.5% and the high-shear specimen reached a drift ratio of 6.5%. The specimens both reached displacement ductility demands above 5, demonstrating the system is appropriate for use as a bridge column in seismic regions. The curvature profiles for both specimens showed the hybrid shell prevented localized yielding of the steel fibers, which allowed for an efficient distribution of plasticity along the column height and enhanced displacement ductility. The results indicate that HCFFT columns can achieve high inelastic deformations under simulated seismic loading without substantial degradation of stiffness. It is anticipated that this large-scale experimental data will inform future research on the design and manufacturing process of HCFFT elements and encourage further experimental and analytical studies.